The use of carbon nanotubes (CNT) or of CNT bundles to manufacture through vias or chip interconnects has already been provided, especially to provide a complement or even an alternative to the use of copper. Indeed, the latter is not adapted when minute sizes are involved. CNTs further have the necessary properties, such as a low electric resistance, enabling to provide the best electric conductivity between the different chip levels,
A via is a cavity enabling to create a connection between conductive plates. The electric lines formed on the plates create the connection between vias, Conductive plates are made of a metal, such as aluminum, and are separated by an insulating layer having the cavity forming the via dug therein.
The miniaturization of electronic devices makes the use of copper quite problematic since copper causes difficulties due to eleetromigration when current densities become too high. Architectures formed of copper lines and vias thus show their limits in integrated circuits having a resolution close to 22 nanometers.
As illustrated in FIGS. 1 and 2, the use of CNTs for ensuring the connection between conductive tracks has been provided, by replacing copper or tungsten vias with CNTs (Katagiri et al., Interconnect Technology Conference, 2009,IEEE International 1-3 Jun. 2009,pp. 44-46; Yokoyama et al. Japanese Journal of Applied Physics, Vol. 47, No 4, 2008,pp. 1985-1990). However, this method does not enable to totally do away with copper, the connection between vias being always ensured by a copper line. Electromigration-related issues are thus not totally suppressed.
Document US 2008/0042287 describes an electronic device in which the connections are at least partially ensured by CNT bundles. The via is covered with a layer of conductive material on which another CNT bundle can be deposited and directed along the line direction. However, the vias and the lines are not formed from the same CNT bundle.
Document US 2006/0212974 discloses an electronic device comprising CNT bundles prepared inside of the via, and then redirected along another direction to connect two conductive layers of two different levels. There are no connections between vias.
Document CN 101562148 relates to a method for creating vertical CNT connections by deposition of a CNT solution on a conductive layer. In this device, two conductive layers of different levels are connected by means of CNT bundles.
Another technology is based on the same concept of CNT vias, but comprises using metal blocks to change the orientation of the CNTs and thus form the horizontal lines (FIG. 3). It is however difficult to control the deposition of a catalyst and the CNT growth along two perpendicular directions on two surfaces of a metal block (FIG. 4). Another disadvantage of this technique is the repeated crossing of many CNT—metal interfaces to ensure the conduction.
Document US 2009/0294966 describes vertical CNT vias ensuring the electric connection between two conductive layers, but also horizontal CNT lines providing an electric connection between vias. This involves two separate bundles directed along two different directions. The CNT bundles coming from the via do not enable to form the line.
These different approaches imply controlling the CNT growth within smaller and smaller cavities, thus raising the issue of the CNT bundle density. Indeed, just like the homogeneity of their properties and of their orientation, the control of the CNT density is of major importance to provide good electric connections in nanoelectronics. High CNT densities are thus indispensable.
Hata and co-workers (Hayamizu et al, Nature nanotechnology, Vol. 3, 2008, 289-294) have recently revealed an organizing and densifying effect capable of being obtained by dipping of a film of scattered CNTs in an alcohol solution. Indeed, when the CNT film is dipped into the alcohol bath, perpendicularly to the surface thereof, and then dried, the CNTs gather and align. Due to the surface tension of the liquid and to the strong Van der Wools interactions, the CNTs achieve a structure close to that of graphite. No disassembly of the CNTs has been observed after densification. However, Hata only obtains structures formed of CNTs directed along the same direction, which thus limits possible applications.
The present invention comes from the search for technical solutions especially enabling to do away with the use of metals and implementing simple manufacturing processes.